Michael Mosley is arguably the most famous human-health guinea pig on the planet.

The BBC journalist, doctor and author of the best-selling 5:2 diet has been studying health and the human body for the past 20 years.

But for all his knowledge and self-experimentation, the self-confessed "sugar addict" has not been particularly healthy.

"I needed to be told I was diabetic to change, despite everything I knew," he says.

Instead of resorting to medication, Mosley decided to get drastic with his diet and see whether he could effect any change.

Turns out he could.

Through intermittent fasting, upping his greens and shifting the way he exercises, he has lost 12 kilograms and his blood sugar has returned to normal. "I can fit into a dinner jacket I haven't worn since I was 25 and I'm enjoying life," says Mosley, who was in Australia this week to promote the release of his book as well as his new BBC documentary series, What's Your Body Hiding.

The basic concept of intermittent fasting, where for two days of the week you restrict your calorie intake to about 2500 kilojoules a day, is that it gives your body a break from processing food and a period where your blood is not filled with glucose.

The diet, which Mosley insists he was initially sceptical about, is not the only interesting discovery he has made through his research for the series.

Some of the others relate to fairly common knowledge, for instance, that we have to drink two litres of water a day or that eggs raise your cholesterol: "Now we know that's absolute rubbish," he says.

Other discoveries are more surprising.

We need five small meals a day

This is "completely, awfully, terribly false," Mosley says.

The idea behind eating regularly is that we speed up our metabolic rate and prevent the body from going into starvation mode. But the body does the opposite, he says.

The origins of this myth come from a study done in the 1950s, when a group of young men survived on approximately half their normal calories for six months.

They lost significant amounts of weight, but while their body fat went down to 5 per cent they also started to experience significant problems.

Relatively short periods of going without food, however, is a different story, Mosley says, and can have a positive effect on us - physiologically and psychologically.

Doctors know it all

While he was studying to become a doctor, Mosley was surprised to hear that, within 15 years of completing his six-year degree, half of what he had learnt would be out of date.

For this reason, he says, exempting those who are specialists or make a concerted effort to keep abreast of the latest science, many doctors lack knowledge in certain areas.

Nutrition and weight loss is one. In fact, he says during his years of training he was required to attend just one class on nutrition.

Despite this, and although some doctors are open-minded about the latest research, "some are happy to pontificate about subjects they know nothing about".

He mentions one study comparing various methods of weight reduction where the group who received advice from their GP actually put on weight.

Sugar is the devil in disguise

In a media briefing this week, Mosley said he disagreed with the stance of I Quit Sugar author and host of the event, Sarah Wilson.

"Sugar is one of my greatest addictions," he acknowledges. "Pretty much every tooth in my mouth has been drilled and replaced. If there's chocolate or biscuits in the house, I'll eat them."

In this sense, he says: "I do generally agree that we eat far too much of it."

That said, he feels sugar has become a "massive thing" and is wary of being "evangelical" about it.

"Do we know that fructose is as demonising as we say? No, the evidence is contradictory."

Besides, he believes it's not about completely avoiding foods, but forgiving yourself when you do falter, being aware of the impact of certain foods and "knowing you'll be constantly tempted and finding strategies around it".

Mosley's strategy involves no longer keeping biscuits or chocolate in the house.

Exercise is the best way to lose weight

"Exercise is a bad form of weight loss," Mosley says, pointing to research on compensatory eating and relaxing, where "basically you're knackered, so you sit down" for the rest of the day.

The problem with people believing that exercise is a good way to lose weight is that they get disenchanted and stop doing it, he explains.

This doesn't mean we shouldn't exercise.

According to Mosley, the real benefits are the effect exercise has on insulin sensitivity and aerobic fitness. "Which means a longer and healthier life," he says.

There's "preliminary" research that high-intensity interval training burns more fat, so "you will look more gorgeous at the beach".

But for those who don't do the recommended daily amount of exercise - about 80 per cent of Australians - Mosley wanted to know "what's the least you can probably do".

"One of the gurus I spoke to said you can get most of the benefits from three minutes a week," he says. "I was absolutely sceptical about it."

Mosley now does a short, sharp workout, pushing as hard as he can for 20 seconds, taking a break and repeating. The entire thing takes him a measly four minutes.

The effects of these quick hits of exercise persist for up to 36 hours after, he says.

Mosley has also increased his incidental activity. Just taking the stairs and getting up regularly has a surprising impact on fat and blood sugar levels.

"We need to move every 30 minutes," he says. "Get off your arse and go for a short stroll."

Everyone needs to eat breakfast

Not true, Mosley says.

He mentions studies where some people, when they are forced to eat breakfast, actually put on weight. "It depends on what your body likes to do," he says.

Which is why Mosley ultimately believes in becoming your own guinea pig. Depending on our own physical make-up and routine, we reap benefits differently. It's a matter of absorbing the information and trying it on for size.

But if you're making a change or trying to break a bad habit, don't expect to be transformed within 21 days.